Radio Frequency amplifier help

Discussion in 'Wireless & RF Design' started by mohiuddin1111, Jun 17, 2013.

  1. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    Guys, i am trying to make a boat with air-propellers.
    I have to use a cheap car transmitter-receiver . which is 40mhz and transmitter is only 3v.
    Its range is 20m around. i badly need to increase the effective range.
    I am using a good pair of antenna. please give advice/links/tips/any-site-to-discuss-about-it to increase the range.
    Any means? like increase transmitter signal strength , receiver sensitivity . i cant use yagi or disc antenna.
    plz
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    How much do you need to increase the range to? 25m? 250m? Big difference, there.

    What do you mean by "a good pair of antenna"? Are they directional (or at least the control station directional)?

    Why do you have to use a cheap car transmitter-receiver? It sounds like you are able to put resources into an amplifier, why not put those resources into a more suitable transmitter/receiver pair to begin with?
     
  3. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    First of all, thanks for quick reply.
    1. Need around at least 100m.
    2. I am a simple noob in this regard. but what i can tell, the transmitter i use is portable (hand held) , i use simple long sylinder shaped antennas found in fm radios. i may use directional antennas in the transmitter, but not in the boat as it would be little.
    then please help me to find better antenna for transmitter.
    3. I live in a country where even slightly uncommon/ not-very-common transistors are also hard to find, transiever module is totally/fully unavailable.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    My recommendation would be to look into designs for directional antennas suitable for 40 MHz (which is roughly in the 10 meter band). If you need to increase the range by a factor of 5, then you need to increase the gain in that direction by a factor of about 25, or a gain of about 15dB.

    So you might look for Ham radio sites for antenna ideas in the 10m band and see if you can adapt them to your use. Most of those antennas will probably be physically larger than you want, but there are probably some that will be nice and portable.

    Hams are notorious for building equipment out of scrap parts lying around and that goes double for antennas, so you might be able to build your antenna with very little money and only easy to get items.
     
  5. Tesla23

    Active Member

    May 10, 2009
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    This looks impossible with your constraints. As far as I can see you want to use a simple handheld transmitter to control a remote controlled boat - where I assume the height of the tx is say 1m, the height of the rx is less, and the intervening land / water is pretty flat. The current system gives you 20m and you want 100m. To increase the range by a factor of 5 you have to find another 28dB of system gain (that's right - you need 5^4 power increase). To see how hard this is, you could:

    - increase the height of the tx and / or rx by a factor of 25. (or each by 5 etc..)
    - increase your transmit power by 625 or 28dB.
    - find 28dB of antenna gain - probably impossible in a handheld device at 40MHz.
    - increase your receive sensitivity

    Looking at this from fundamentals, assuming that you have no antenna gain at either end, 100m path with a 1m tx height and 0.5m rx height, gives you a path loss (tx output to rx input) of 86dB. There are a vast array of low cost RF modules that could provide reliable data transmission over this link.
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    Is the power of 5 because of the nearness to the ground?

    At what point would it transition to a square-law relationship (if it does anywhere short of free space)?
     
  7. Tesla23

    Active Member

    May 10, 2009
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    It goes as the fourth power of distance due to the ground reflection, here's a couple of links I found that explain it:
    http://www.isi.edu/nsnam/ns/doc/node218.html
    http://www.ece.mtu.edu/faculty/ztian/ee5530/two_path.pdf

    The first one suggests that the transition would be at 1-2m, but as it only gets to square-law in the far field, and as 1-2m is near field, I suspect it never really does.

    eqn 4.2.9 in the second link is the key equation - and very simple. The loss is also independent of frequnency to a first approximation.
     
  8. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    OK. Will try ham radio sites. Saw some by google search, but, hey give a link to a good one please?
    And, about power, i can increase the power of transmitter from 3v 500mAh upto 12v 6Ah / or even 24v 6Ah. But i cannot directly connect this much voltage to the transmitter. i may use a amplifier with a transmitter?
    or at least increase receiver's sensitivity?? how?
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    What do you mean by "increase the power of transmitter from 3v 500mAh upto 12v 6Ah"?

    3V 500mAh tells you to the (nominal) total energy available from your battery. It says nothing about power. For power, you need the current that the battery can support, which is unrelated to the amp-hour rating.

    Sure you can use an amplifier (if it is legal in your country), but you've said that it is very hard to get even slightly uncommon transistors and that RF transmit/receive modules are completely unavailable. Where are you going to get an RF amplifier from? And how could we possibly recommend something given constraints like that?

    Since cooling the receiver probably isn't an option, the easiest way to increase the receiver's sensitivity would be to replace it with a more sensitive receiver. You could, conceivably, use a preamplifier, but you would have to be careful not to blow out our receiver's front end when you boat was nearby and receiving a strong signal.

    Tesla23 might have some other ideas for improving the receiver sensitivity that might be practical for you.
     
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  10. Tesla23

    Active Member

    May 10, 2009
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    This doesn't make much sense.You need to search around for some introductory material on wireless links.

    You should be able to achieve 100m of range with any radio system that can overcome around 86dB of path loss. So modules like:

    http://dx.com/p/433mhz-wireless-rf-transceiver-module-w-spring-antenna-157030

    https://www.sparkfun.com/products/10153

    These provide over 120dB of system gain so should easily provide the control you want over 100m using simple antennas (e.g. the simple spring antenna provided on the first one should be adequate).
     
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  11. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    Guyz guyz guyz.....
    i am pretty illiterate on RF things u see...
    about the battery i know what mAh/Ah means. but gave it just as an information which might be relevant somehow ??
    it seems the i can get the module from that dx.com ( anything from this site) .
    but the problem is how can i use this thing. i need to control two motor and a light. please help. really feeling helpless here. :(
     
  12. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    anyone guys...
     
  13. absf

    Senior Member

    Dec 29, 2010
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    Normally I use an encoder before the TX module and a decoder after the RX module. Google for "PT2262 PT2272 datasheet" and see what you get.

    Or you can program a PIC as an encoder or decoder....

    http://jap.hu/electronic/codec.html

    Allen
     
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  14. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    i am getting scared visiting ur provided link. Too much complex to start with for beginners like me.
    can u give me a link or any diagram or basic idea of how can i use this module what @tesla23 already mentioned above already??
     
  15. absf

    Senior Member

    Dec 29, 2010
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    The module introduced by tesla23 is a transceiver. It can be used as a transmitter or as a receiver. The encoder that I mentioned is the same as the ones used in older cars. It can control 2 or 3 buttons so each button is controlling one channel. On the receiving side the decoder will convert the received signal back to its own channel again.

    How to interface the transceiver to the encoder/decoder chip? That you have to get the manual and study it yourself as I've never used them before. But anyway I have found some schematics of a 4-channel RC system that might explain to you how they work as attached.

    I suggest you learn the principles first before you jump into the final schematic. Use the RF Remote Control that you already have and add in the encoder/decoder and make it able to light up 4 LEDs on the receiving side first before you try to attempt the transceiver that will go >100M.

    http://www.circuitstoday.com/remote-control-circuit-through-rf-without-microcontroller

    Allen
     
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  16. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    Thanks alot.
    i did abit reading and searching internet. but still confused.
    saw a few manuals and datasheet .
    but, please help me to clear things a bit.
    1. Do all transceiver modules have serial mode , switch mode? i need switch mode.

    2. Do all of them has address pin ? i need to have address pin as i will use 3~4 modules as receiver with one module as transmitter.

    3. Guys i need a transceiver module having switch mode and address pin

    I know guys that you are here to help, not to render service. But i so badly need your help .
     
  17. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    guys??....
     
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